Binder for powder metallurgical compositions

ABSTRACT

A binder for metallurgical powder compositions for powder metallurgy (P/M) applications includes styrene/maleic anhydride copolymers and their derivatives. Addition of such binders has improved resistance to dusting, and has improved flow properties of the compositions, even in high relative humidity environments. The compositions can be compacted either at cold or warm temperatures. A mechanical strength of a sintered product containing the binder-treated mix is similar to that of sintered products without the binder.

This application claims benefit of U.S. Provisional Application60/571,490 filed May 17, 2005.

FIELD OF THE INVENTION

The present invention relates to powder metallurgical compositions, andin particular to copolymer binders for ferrous powder compositionshaving binding properties and yielding powder formulation havingimproved dust resistance and flow.

BACKGROUND OF THE INVENTION

Processes for producing metal parts from ferrous powders using powdermetallurgy (P/M) techniques are well known. Such techniques typicallyinvolve mixing ferrous powders with alloying components such asgraphite, copper or nickel in powder form, filling the die with thepowder mix, compacting and shaping the compact by the application ofpressure, and ejecting the compact from the die. The compact is thensintered to develop metallurgical bonds by mass transfer under theinfluence of heat. It is known that the presence of an alloying elementenhances the strength and other mechanical properties in the sinteredpart compared to the ferrous powders alone. When necessary, secondaryoperations such as sizing, coining, repressing, impregnation,infiltration, machining, joining, etc. are performed on the P/M part.

It is common practice to add a lubricant to the powder mix (i.e.metallurgical powder composition) to improve the compaction. Thelubricant is required mainly to reduce the friction between metalpowders and die walls. By ensuring a good transfer of the compactingforce during the compaction stage, it improves the uniformity ofdensification throughout the part. Furthermore, it also lowers the forcerequired to remove the compact from the die, thus reducing die wear andyielding parts with good surface finish.

In addition to the lubricant, other alloying powders and additives arealso often added to the basic metal powders to achieve desired physicaland metallurgical properties in the sintered products. These alloyingpowders and other additives (secondary powders) typically differ fromthe basic metal powders in particle size, shape and density making thesepowder mixtures susceptible to the undesirable separatory phenomena ofsegregation, and dusting, which is prone to happen, for example, duringhandling, storage or transfer of the mixtures. It will be appreciatedthat uniformity of the powder mixture is typically required to ensureconsistent material properties of the sintered product. Dusting is aserious health concern. Dusting occurs when lighter and finer particlesare entrained in air. The air-borne particles may be inhaled resultingin various health risks. In order to prevent segregation and dusting,organic binders can be added to the powder mixtures to bind the finealloying powders and additives to the primary metallic powders.

Various organic binding agents have been suggested to preventsegregation and dusting of these powder mixtures. For example, in U.S.Pat. No. 4,483,905, it has been found that segregation and dusting canbe reduced or eliminated if the powder contains a binding agent in solidor liquid state. It is preferred to add to the metal powder one of theagents polyethylene glycol, polypropylene glycol, glycerine, andpolyvinyl alcohol, in a quantity of 0.005-0.2 percent by weight. U.S.Pat. No. 4,676,831 teaches iron based powder mixtures, which except ironor steel powder and one or more alloying elements in powder form alsocontain an addition of up to 0.5% of talloil to preventsegregation/dusting. In U.S. Pat. No. 5,069,714, Gosselin discloses animproved metallurgical powder composition of a ferrous powder and atleast one of an alloying powder, a lubricant or other additive. Lining,dusting and/or segregation of the composition is prevented by use of apolyvinyl pyrrolidone binding agent. In U.S. Pat. No. 5,286,275,Murakami discloses a powder mixture for powder metallurgy comprising astarting powder for powder metallurgy containing a metal powder, apowder of physical property improving ingredients and a lubricant and,blended therewith as a binder, a synthetic styrenic rubber copolymercomprising: 5 to 75 parts by weight of styrene and 95 to 25 parts byweight of butadiene and/or isoprene, as the monomer ingredient or ahydrogenation product thereof. The binder can suppress the segregationof the physical property improver and the lubricant, as well as dustingupon handling the powder. Also, for warm pressing applications, Lukdiscloses in U.S. Pat. No. 5,429,792 an improved metallurgical powdercomposition capable of being compacted at elevated temperaturescomprising an iron-based powder, an alloying powder, a high temperaturecompaction lubricant, and a binder. The selected binders of thisinvention permit the bonded powder composition to achieve increasedcompressibility in comparison to unbonded powder compositions whilereducing dusting and segregation of the alloying powder.

These binders are effective in preventing segregation and dusting, butthey may adversely affect other physical properties such ascompressibility and flow of the powder. Thus, a few patents providespecific binders for reduction or elimination of segregation and dustingwhile at the same time resisting degradation of physical properties ofthe powders and metallurgical properties of the sintered output. Forexample, in U.S. Pat. No. 5,432,223, Champagne discloses a novelhigh-performance binder system for the fabrication of segregation-freeiron based powder blends. The blends are prepared by using a bindersystem comprising thermoplastic resin polyvinylpyrrolidone (PVP) and asuitable compatible plasticizer such as polyethylene (PEG), and optionalsolid lubricants. The binder system enables the manufacture ofsegregation-free iron-based powder blends with high flow rate andcompressibility, enhanced apparent density, green strength andtransverse rupture strength, and low dimensional variations compared tounbonded powder blends and to blends made with PVP or PEG only as thebinder. Also, in U.S. Pat. No. 5,976,215, Satoshi discloses aniron-based powder mixture for powder metallurgy, comprising: aniron-based powder, and from 0.05 to 0.5% by weight of a thermoplasticresin powder which comprises 50% or more by weight of units of at leastone monomer selected from the group consisting of acrylic esters,methacrylic esters, and aromatic vinyl compounds, and whose averageprimary particle size is from 0.03 to 5 μm, whose average agglomerationparticle size is from 5 to 50 μm, and whose average molecular weight isfrom 30000 to 5000000. The resin powder is used as a non-binder powderto further improve the flowability of the iron-based powder mixture

There remains a need for another binder agent that mixed with ametallurgical powder mixture produces a metallurgical powdercomposition, wherein the binder agent imparts on the metallurgicalpowder composition: reduced segregation and dusting, and improved flowcharacteristics, without reducing the sintered properties of thesintered pieces.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a binder suitable for use ina metallurgical powder mixture.

There is provided herein a metallurgical powder composition comprising ametal powder and from about 0.01 to about 3 wt. % of a specific binderbased on the total weight of the metallurgical powder composition.Preferably the specific binder is from about 0.05% to about 1.5% of theweight of the metallurgical powder composition. This binder may beadmixed to the metal powder in a solid state (comminuted, usually as apowder) and subsequently melted to bind the secondary powders to theprimary powder. It can also be admixed in emulsion, or in solution or inthe melted state. The metallurgical powder composition may furthercomprise other solid lubricants or binders to improve thecompressibility, lubrication performance, flowability, and/or thesegregation of the metallurgical powder composition.

Typically, the metal powder is an iron-based powder. Examples ofiron-based powders are pure iron powders, powders of iron pre-alloyedwith other alloying elements, and powders of iron to which such otherelements have been diffusion-bonded. The metallurgical powdercompositions may further contain powders of such alloying elements inthe amount of up to 15 wt. % of said metallurgical powder composition.Examples of alloying elements include, but are not limited to, elementalcopper, nickel, molybdenum, manganese, phosphorous, metallurgical carbon(graphite) and alloys of the above with or without iron.

The specific binder of the invention is a styrene/maleic anhydridecopolymer and/or one of its derivatives. In some embodiments thecopolymer binders of the invention are soluble in standard solvents.Derivatives include, but are not limited to, partially esterifiedstyrene/maleic anhydride copolymers and styrene/maleimide copolymers,and mixtures thereof. The copolymer binder of the invention may have astyrene/maleic anhydride ratio that provides a glass transitiontemperature above the compaction temperature.

Metallurgical powder compositions of the invention can be compacted in adie to produce a green piece. The green piece can subsequently be heattreated at temperatures below 500° C. and/or sintered according tostandard powder metallurgy techniques to produce a part.

The use of styrene/maleic anhydride copolymer, or one of its derivativesas a binder for metallurgical powder compositions is also provided.

A method of producing a compactable metallurgical powder composition isalso provided. The method involves adding from about 0.01 wt. % to about3 wt. % of one of a styrene/maleic anhydride copolymer and a derivativethereof to a metallurgical powder mixture, to produce a compactablemetal powder composition. The method may further involve steps of:compacting to form a green piece, by either warm or cold compaction;curing the green piece to allow for green machining; and sintering thegreen piece (cured or not). The powder composition, compact, cured greenpiece, and sintered output are part of the invention provided.

A kit comprising a styrene/maleimide copolymer and/or a derivativethereof having a molecular weight between about 1000 and 30000, ametallurgical powder composition, and instructions for carrying out themethod.

DETAILED DESCRIPTION OF THE INVENTION

Several binder-treated powder compositions were prepared and tested forthe fabrication of ferrous compacts for P/M applications. Exemplarymetal powders suitable for the purpose of the present invention includeiron-based powders used in the P/M industry, such as pure iron powders,pre-alloyed iron powders (including steel powders) and diffusion-bondediron-based powders. Substantially any ferrous powder having a maximumparticle size less than about 600 microns can be used in the compositionof the invention. Typical ferrous powders are iron and steel powdersincluding stainless steel and alloyed steel powders. ATOMET® steelpowders manufactured by Quebec Metal Powders Limited of Tracy, Quebec,Canada are representative of such iron and steel powders. TypicalATOMET® powders contain in excess of 99.6 wt. % iron and pre-alloyedmetals, less than 0.3 wt. % oxygen and less than 0.1 wt. % carbon, andhave an apparent density of 2.50 g/cm³ or higher, and a flow rate ofless than 30 seconds per 50 g.

Optionally, the iron-based powders can be admixed with alloying powdersin the amount of preferably less than 15 wt. %. Examples of alloyingpowders include, but are not limited to, elemental copper, nickel,molybdenum, manganese, phosphorus, metallurgical carbon (i.e. graphite)and alloys of the above, with or without iron.

Powder compositions of the invention include a specific binder in anamount from about 0.01 wt % to about 3 wt % based on the total weight ofthe composition, preferably from about 0.05 wt. % to about 1.5 wt. %.This specific binder may be admixed to the metal powder in a solid state(e.g. comminuted to a powder) and subsequently melted to bind thesecondary powders to the basic metal powder. It can also be admixed inemulsion, or in solution or in the melted state. The admixture may becarried out in a single operation or step, or in several steps. Thecomposition may further comprise other solid lubricants or binders orflow agents to further improve either the compressibility andlubrication performance, the flow and/or the segregation of the powdermixes. Additionally, the composition may contain one or more additionalbinders that can chemically interact with the specific binder, or cangive rise to an association product, also known as an interpolymercomplex, by strong intermolecular acid-base interactions, in order toimprove the strength of compacted parts, as disclosed in applicant'sU.S. Pat. No. 5,980,603, which is incorporated herein by reference.

The specific binder is a styrene/maleic anhydride copolymer, and/or oneor more of its derivatives. Derivatives include, but are not limited to,partially esterified styrene/maleic anhydride copolymers (preferably 20to 90%), esterified styrene/maleic anhydride copolymers andstyrene/maleimide copolymers, and combinations of the above.

The copolymer binder has a weight-average molecular weight (Mw) between1,000 and 30,000. In some embodiments the Mw of the binder is preferablybetween about 2,000 and 25000, and in some embodiments is between about5,000 and 10,000. In some embodiments the copolymer binder has astyrene/maleic anhydride ratio, between 1:1 and 8:1. In some instances,the styrene/maleic anhydride ratio is selected to provide a binderhaving a glass transition temperature between about 30 and 200° C.,preferably less than about 150° C.

The copolymer binder of the invention is soluble in standard solvents,which makes it possible to prepare the binder-treated powder compositionusing spray coating techniques, or by other known techniques.

The copolymer binders of the invention can be produced by thepolymerization of styrene and maleic anhydride. Partially esterifiedstyrene/maleic anhydride copolymers are obtained by partialesterification of styrene/maleic anhydride copolymers with compoundscontaining hydroxyl functional groups. Styrene/maleimide copolymers canbe obtained by reacting styrene/maleic anhydride copolymers withcompounds containing primary amino functional groups. These copolymers,bond the fine secondary powders to the basic powder, thus improving dustresistance of the metallurgical powder composition. These copolymers inconjunction with an additional binder provide improved green strength ofthe cured green piece according to the mechanisms explained in U.S. Pat.#5,980,603. Furthermore these copolymers dissolve in readily availablesolvents (such as acetone), and therefore can be applied to themetallurgical powder in a wide range of known techniques.

Examples of commercially available styrene/maleic anhydride copolymersthat are suitable as P/M binders in accordance with the presentinvention include Sartomer's styrene maleic anhydride copolymers andtheir derivatives, which are commercially available from Atofina.Esterification of the styrene/maleic anhydride copolymers makes thebinder more hydrophobic, resulting in less sensitivity to high humiditylevels, and improving solubility in numerous readily available solvents.

The metallurgical powder compositions of the invention can be compactedunder conventional powder metallurgy conditions. The compactingpressures are typically lower than 85 tsi and more specifically between10 and 60 tsi. The compacting temperature suitable with the compositionsof the invention is below about 200° C., preferably below 180° C., andmore preferably between 40 and 160° C. In some embodiments it ispreferable that compaction be applied at a temperature above the glasstransition temperature of the copolymer binder, to improvecompressibility of the powder metallurgical composition. Aftercompaction, green parts can be submitted to a low temperature heattreatment below 500° C., so as to increase further the mechanicalstrength of the parts.

EXAMPLE 1 Flow

Tests were conducted to evaluate the flowability of binder-treatedblends containing different binders of the invention. In this example, astyrene/maleic anhydride copolymer (Sartomer SMA® 1440) and a partiallyesterified styrene/maleic anhydride copolymer (Sartomer SMA® EF-40)having weight-average molecular weights close to 7,000 and 10,000respectively (available from Atofina) were evaluated as binders. Thesetwo binders are referred as S1 and S2 in the text. Two binder-treatedpowder compositions were prepared by dissolving 0.2 wt. % of the bindersin a solvent, by mixing this solution with a powder mixture, using aknown spray coating technique, and finally by evaporating the solvent.The powder mixture was 97.4 wt. % ATOMET 1001 steel powder (Quebec MetalPowders Ltd.), 0.6 wt. % graphite powder (South Western 1651), 2 wt. %copper powder (MD 165) and 0.55 wt. % of atomized ACRAWAX C powder fromLonza Inc. (EBS). The flowability of the two binder-treated powdercompositions of this invention was compared with the that of a drymixture, referred as Control Mix. The Control Mix consisted of 97.4 wt.% ATOMET 4201 steel powder (Quebec Metal Powders Ltd.), 0.6 wt. %graphite powder (South Western 1651) and 2 wt. % copper powder (MD 165)and 0.75 wt. % of atomized ACRAWAX C powder from Lonza Inc. (EBS). Theapparent density (MPIF Standard 04) and flow rate (MPIF Standard 03) ofthe powder compositions were determined.

The results illustrated in Table 1 show that adding eitherstyrene/maleic anhydride or esterified styrene/maleic anhydridecopolymer binders to the dry mixture, produces powder compositions (thebinder-treated Mixes 1 and 2) that are free flowing, whereas the Controlmix itself is not free flowing, even though the control mix contains asame amount (0.75%) of organic content (lubricant), as thebinder-treated Mixes 1 and 2. TABLE 1 Physical properties of the controland binder-treated mixes at normal relative humidity level andtemperature Relative Humidity (50%) - Temperature (25° C.) ApparentBinder density g/cm³ Flow rate s/50 g Control mix No binder * No flowBinder-treated mix 1 S1 2.90 33 Binder-treated mix 2 S2 2.90 35*Due to its non free flowing character, it cannot be measured accordingto MPIF standard 04

EXAMPLE 2 Flow and Separatory Properties

Tests were conducted to evaluate the binding efficiency of the binder ofthe invention. In this example, a partially esterified styrene/maleicanhydride copolymer having a weight-average molecular weight close to7,000 (Sartomer SMA® 1440) was evaluated as a binder. A binder-treatedmetallurgical powder composition (Binder-treated Mix) was prepared bydissolving 0.35 wt. % of the partially esterified styrene/maleicanhydride binder in a solvent, by mixing this solution with a powdermixture, using a known spray coating technique, and finally byevaporating the solvent. The powder mixture was 97.08 wt. % ATOMET 4201steel powder (Quebec Metal Powders Ltd.), 0.92 wt. % graphite powder(South Western 1651), 2 wt. % copper powder (SCM 500RL) and 0.65 wt. %of atomized ACRAWAX C powder from Lonza Inc. (EBS). The dustingresistance of this binder-treated powder composition was compared withthe behavior of a dry mixture, referred as Control Mix. Control Mixconsisted of 97.08 wt. % ATOMET 4201 steel powder (Quebec Metal PowdersLtd.), 0.92 wt. % graphite powder (South Western 1651) and 2 wt. %copper powder (MD 165) and 0.75 wt. % of atomized ACRAWAX C powder fromLonza Inc. (EBS). The apparent density (MPIF Standard 04) and flow rate(MPIF Standard 03) of the powder compositions were also determined.Finally, the effect of humidity on the flow and the apparent density ofthe binder-treated powder composition of the invention were alsoevaluated.

The effect of the binder of the invention on the graphite and copperdusting resistances were determined by fluidization with a stream of gas(in this case air). Air was directed at a constant flow rate of 6.0liters/minute for ten minutes at the bottom of a 2.5 cm diameter tube inwhich the test material was placed. This causes finer secondary powders,such as graphite, to be entrained, as a result of a largesurface-to-volume ratio, and low specific gravity (in the case ofgraphite), and to be deposited in the dust collector. The mixtureremaining on the screen plate was then analyzed to determine therelative amount of carbon and copper, which is a measure of theresistance to carbon and copper dusting when expressed as a percentageof the pre-test concentration. The apparent density and flow rate of thepowder compositions were determined. The effect of humidity on the flowcharacteristic was assessed by measuring the apparent density of thepowder compositions after exposure for 24 hours at a relative humidity(RH) of 90% and a temperature of 32° C. The flow rate was not measuredduring these experiments; only the attribute ‘free’ flow or ‘no’ flowwas given to the powder composition.

As given in Table 2, the graphite and copper dusting resistancesprovided by the Binder-treated Mix is significantly improved as comparedto the Control Mix containing no binder. TABLE 2 Dusting resistance ofthe control and binder-treated mixes Graphite dusting Copper dustingControl Mix 33 16 Binder-treated Mix 91 39

It can also be observed in respect of Table 3, that the flow rate of thebinder-treated mix containing the binder of the invention issignificantly improved compared to the Control Mix containing no binder.A significantly lower apparent density is also measured with the ControlMix. TABLE 3 Physical properties of the control and binder-treated mixesat normal relative humidity level and temperature Relative Humidity(30%) - Temperature (25° C.) Apparent density g/cm³ Flow rate s/50 gControl mix 3.29 36 Binder-treated mix 3.40 22

As shown in table 4, the Binder-treated Mix containing the binder of theinvention remains free flowing after exposure for 24 hours at a humiditylevel of 90%. It will be also noted that the high relative humiditylevel does not affect the apparent density of the metallurgicalcomposition containing the partially esterified styrene/maleic anhydridebinder. TABLE 4 Physical properties of the binder-treated mix at highrelative humidity level Relative Humidity (90%) - Temperature (35° C.)Apparent density g/cm³ Flow Binder-treated mix 3.37 Free flow

EXAMPLE 3 Effect of Heat Treatment

In a third example, a partially esterified styrene/maleic anhydridecopolymers having a weight-average molecular weight close to 7,000(Sartomer SMA® 1440) was evaluated as a binder. Three powdercompositions were prepared. The first powder composition was prepared bymixing 97.4 wt. % ATOMET 4601 steel powder (Quebec Metal Powders Ltd.)with 0.6 wt. % graphite powder (South Western 1651) and 2 wt. % copperpowder (MD165) and 0.75 wt. % of atomized ACRAWAX C powder from LonzaInc. This dry mixture is called REF Mix. The second powder compositionwas prepared by dry mixing 97.4 wt. % ATOMET 4601 steel powder (QuebecMetal Powders Ltd.) with 0.6 wt. % graphite powder (South Western 1651)and 2 wt. % copper powder (SCM 500RL) and 0.4 wt. % of oxidizedpolyethylene homopolymer lubricant powder (Acumist A6 from Honeywell).This dry mixture is called Control Mix. The third powder composition wasprepared by dissolving in a solvent 0.1 wt. % of the same partiallyesterified styrene/maleic anhydride binder described in example 1, bymixing the binding solution with the dry mixture called Control mix, andby evaporating the solvent. This third powder composition is calledBinder-treated Mix.

Rectangular bars (3.175×1.270×0.635 cm) were pressed at 25° C. and 45tsi in a floating compaction die. Some bars were heat treated in air at175° C. during 1 hour. Other bars were sintered in a 90% nitrogen basedatmosphere at 112° C. for 30 minutes. Cured green densities andmechanical strengths (transverse rupture strength (TRS) according toMPIF 15 Standard) were evaluated. The apparent density (MPIF Standard04) and flow rate (MPIF Standard 03) of the powder compositions werealso determined. The results are reported in Tables 5, 6 and 7. TABLE 5Physical properties of the dry and binder-treated mixes at normalrelative humidity level and temperature Conditions: Relative Humidity(30%) - Temperature (25° C.) Mixture Apparent density g/cm³ Flow rates/50 g REF Mix 2.97 36 Control mix —* No Flow Binder-treated mix 2.97 36*Due to its non free flowing character, it cannot be measured accordingto MPIF standard 04

TABLE 6 Physical and mechanical properties of the dry and binder-treatedmixes after curing. Green strength after Green density g/cm³ curing at175° C. Ref Mix 7.06 2575 Control mix 7.06 7000-8000 Binder-treated mix7.06 7000-8000

TABLE 7 Sintered properties of the dry and binder-treated mixes aftersintering. Binder- Ref Mix treated Mix TRS after sintering, psi 184 828184 468 Sintered density g/cm³ 6.97 7.0 Dimensional change from die 0.190.15 size (%)

The results illustrated in Table 5 show that adding esterifiedstyrene/maleic anhydride copolymer binder to the Control Mix, produces apowder composition (the binder-treated Mix) that is free flowing,whereas the Control mix itself is not free flowing. In addition, whileexhibiting a green density similar to the Ref Mix containing the EBSpowder, the binder-treated mix yield parts having similar high curedgreen strength (after curing at 175° C. during 1 hour) to that of theControl mix shown in Table 6.

The fact that the control and binder-treated mixes containing theoxidized polyethylene homopolymer powder have a higher cured greenstrength than conventional powder compositions containing, for exampleEBS powder, may be attributed to the polymer flowing into open poresduring the heat treatment, leading to a network of lubricantsufficiently strong to enhance the cured green strength.

The powder composition containing the binder of the invention has theadvantage of being free flowing while maintaining a high cured greenstrength after curing at moderate temperature. Finally, as shown inTable 7, the binder of the invention does not hinder the sinteringprocess of powder metallurgical compositions. Indeed, the mechanicalstrength after sintering the binder-treated mix is similar to that ofthe dry REF mix containing the EBS powder.

The invention has therefore been described in relation to a novelbinder, a metallurgical powder composition including the binder, acompact, and a cured green piece formed therefrom, and a sintered metalpiece product. A method of producing the above is also described.

1. A metallurgical powder composition comprising a metal powder and fromabout 0.01% to about 3% of the weight of the metal powder of one of astyrene/maleic anhydride copolymer binder and a derivative thereof. 2.The composition of claim 1 wherein the content of said copolymer is from0.05 wt. % to about 1.5. wt. %.
 3. The composition of claim 1 furthercomprising an alloying element powder in the amount of up to about 15wt. % of the composition.
 4. The composition of claim 3 wherein saidalloying element is one or more selected from the group consisting ofelemental copper, nickel, molybdenum, manganese, phosphorus,metallurgical carbon and alloys of the above, with or without iron. 5.The composition of claim 0.1 further comprising a lubricant.
 6. Thecomposition of claim 1 further comprising a second binder.
 7. Thecomposition of claim 6 wherein the second binder is selected tochemically interact with the styrene/maleic anhydride copolymer binderto produce an association product, by strong intermolecular acid-baseinteractions.
 8. The composition of claim 1 wherein said copolymer is apartially esterified styrene/maleic anhydride copolymer.
 9. Thecomposition of claim 1 wherein said copolymer is a styrene/maleimidecopolymer.
 10. The composition of claim 1 wherein said copolymer has aweight-average molecular weight between 1,000 and 30,000.
 11. Thecomposition of claim 8 wherein said copolymer has a weight-averagemolecular weight between 5,000 and 10,000.
 12. The composition of claim1 wherein said copolymer has a glass transition temperature between 30and 200° C.
 13. The composition of claim 1 wherein said copolymer hasstyrene/maleic anhydride ratios between 1:1 and 8:1.
 14. The compositionaccording to claim 1 wherein said ferrous powder has a maximum particlesize less than about 600 microns.
 15. The composition according to claim1 adapted to be compacted at temperatures below 200° C. in a die to formparts that are subsequently heat treated at temperatures below 500° C.and/or sintered according to standard powder metallurgy techniques. 16.A use of styrene/maleic anhydride copolymer and/or a derivative thereof,as a binder for binding a metallurgical powder mixture to form acompactable metal powder composition.
 17. The use according to claim 16wherein from about 0.01 wt. % to about 3 wt. % of the styrene/maleicanhydride copolymer or derivative is added to the metallurgical powdermixture.
 18. A method of producing a compactable metal powdercomposition, the method comprising: providing a metallurgical powdermixture; and adding from about 0.01 wt. % to about 3 wt. % of astyrene/maleic anhydride copolymer and/or a derivative thereof to themetallurgical powder mixture, to produce a compactable metal powdercomposition.
 19. A product of the method of claim
 18. 20. A method ofproducing a green piece, the method comprising: placing a compactablemetal powder composition according to claim 1 in a die; pressing thecompactable metal powder composition to form a green piece.
 21. Themethod according to claim 20 wherein pressing is applied at atemperature below 200 degrees Celsius.
 22. The method according to claim20 further comprising curing the green piece at a temperature below 500degrees Celsius.
 23. A product of the method of claim
 20. 24. A productof the method of claim
 22. 25. A method of producing a metal piece, themethod comprising sintering the green piece according to claim
 20. 26. Amethod of producing a metal piece, the method comprising sintering thegreen piece according to claim
 22. 27. A kit comprising: astyrene/maleic anhydride copolymer or a derivative thereof having amolecular weight between about 1,000 and 30,000; a metallurgical powdercomposition; and instructions for carrying out the method of claim 17.